Understanding molecular fingerprints of specific cell types is central for defining lineage development, progression, differentiation and pathophysiological perturbations. This study addressed gene expression profiles in freshly isolated fetal human LSEC as well as these LSEC after cell culture. Comparisons with human umbilical vein endothelial cells (HUVEC) allowed determination of lineage-specific differences. Cell culture allowed identification of differences in phenotype regulation of cells under these conditions. Overall design: Comparisons were made between freshly isolated LSEC (PP cells), LSEC after initial culture (P0 cells) and LSEC after passages (P2 or P3) from 3 donors each. Freshly isolated HUVEC served as controls for comparisons.